The present invention relates to a cement material containing polyarylene thioether fibers and carbon fibers as reinforcing material, as well as molded articles comprising hardened products thereof. Particularly, the present invention relates to a fiber-reinforced cement material curable in an autoclave, as well as molding products comprising hardened products thereof.
Since mortar cement or concrete is poor in strength against bending or impact as molded articles such as wallboards to be used as building materials, roofing materials, pipes for various purposes, plates to be used as pile materials, pillars, etc., cement materials, reinforced with asbesto fibers have been used for obtaining these molded articles.
Fiber-reinforced cement materials have the following advantageous features:
(1) improved in tensile strength, bending strength and impact strength,
(2) improved in deflection property,
(3) improved in cracking resistance, etc.
However, it has been found in recent years that asbestos exhibits carcinogenicity and the use thereof has presented a serious problem in view of public pollution. Although it has been attempted to use glass fibers for the reinforcing fibers as a substitute for the asbestos fibers, the glass fibers involve a drawback of reactivity with alkaline cement thereby tending to cause deterioration with time.
Further, although there have also been proposed other fiber-reinforced cement materials such as those containing organic fibers, for example, cellulose, polyolefin, polyester, polyamide (including polyaromatic amide), polyvinyl alcohol, etc., such fiber-reinforced cement materials are not satisfactory in alkali resistance or heat resistance and involve a problem of deterioration with time or thermal deterioration during autoclave curing (as described in "Fibers and Industry", vol. 41, June, p 14-18, etc.).
While on the other hand, fiber-reinforced cement material using carbon fibers has been developed in recent years in view of the heat resistance and alkali resistance thereof (as disclosed in "Nikkei New Material", 1985, November, p 125-130, etc.). However, although carbon fibers have sufficient tensile strength and bending strength, as well as modulus of elasticity, since carbon fibers are poor in elongation and toughness, no satisfactory effects for improving the deflection property and the impact strength of the molded articles have yet been obtained.
In order to overcome the foregoing problems, the present inventors have made an extensives for various kinds of fibers as substitutes for asbestos fibers and, as the result of the study for the alkali resistance, heat resistance, flame resistance and the economical merit of various kinds of fibers, it has been found that polyarylene thioether fibers can substitute for the asbestos fibers as the reinforcing fibers for cements. That is, the present inventors have found that a cement material reinforced with polyarylene thioether fibers is capable of providing molded articles having an improved deflection property and impact strength and is hardly deteriorated during the autoclave curing required for obtaining dimensionally stable molded articles.
However, the present inventors have also found that the remarkable effect for improving the tensile strength or bending strength can only be attained when polyarylene thioether fibers of specially enhanced modulus prepared by complicated stretching and heat treatments (thus requiring extremely high cost) are adopted. By the way, moduli of general grade polyarylene thioether are usually lower than that of the matrix component (cement component). However, as a result of the present inventors study, it has been found that a fiber-reinforced cement material containing an adequate amount of both of polyarylene thioether fibers and carbon fibers as the reinforcing fibers is curable in an autoclave and capable of providing molded articles improved in tensile strength and bending strength as well as in deflection property and impact strength due to the synergistic effect derived from both of the fibers. The present invention has been accomplished based on these findings.